Electrostatic chucks are employed to support wafers in a variety of semiconductor workpiece processing systems. In a deposition system, for example, an electrostatic chuck may be used to clamp a wafer in place while a thin film is deposited on the wafer. In an etch system, as another example, an electrostatic chuck may be used to clamp a wafer in place while material is being chemically etched from the wafer. These systems typically comprise a reaction chamber, a vacuum pumping system for removing gases from the chamber, a reactant delivery system for conveying chemical reactants to the chamber, and a workpiece support system for holding the workpiece in place during processing.
A typical workpiece support system employs a platen that supports the workpiece during processing. Some systems also utilize electrostatic chucks, which use electrostatic force to hold the workpiece in place. An electrostatic chuck has electrodes that are energized with a clamping voltage, which electrostatically clamps the wafer to the surface of the electrostatic chuck. The electrodes in the electrostatic chuck are coupled to an electrostatic power supply and a controller. The electrostatic power supply receives the control signal from the controller and generates a clamping voltage adapted to clamp the substrate with a clamping force.
Before the process begins, a wafer is transferred into the reaction chamber and is typically placed on lift pins that support the wafer prior to loading onto the electrostatic chuck. The lift pins are then lowered (and/or the electrostatic chuck is raised) such that the wafer rests on the upper surface of the electrostatic chuck rather than on the lift pins. At this time, clamping voltage is applied to the electrostatic chuck to clamp the wafer in preparation of the process. After completion of the process, the clamping voltage is removed to release the wafer from the electrostatic chuck, and the lift pins are engaged to lift the wafer above the surface of the electrostatic chuck. Thereafter, the treated wafer can be removed from the lift pins using a transport mechanism.
Proper positioning of the wafer relative to the electrostatic chuck is important at various times before, during, and after typical semiconductor workpiece processes. For example, it is important to ensure that the wafer is properly loaded onto the electrostatic chuck before applying the clamping voltage. As another example, it may be desirable to determine whether the wafer is clamped or unclamped at certain times. As yet another example, it can be important to ensure that the wafer is properly positioned on the lift pins before proceeding further in the processing cycle.